To avoid safety problems in strongly exothermic reactions, the literature proposes performing these reactions in a microreactor. In microreactors, these reactions are easier to control than in conventional batch reactors or continuous reactors. In addition, it is possible in the microreactor to achieve reaction conditions which are not achievable for safety reasons using conventional methods in the laboratory or on the industrial scale.
Reactions which can lead to safety problems are, for example, gas-liquid reactions, for instance catalytic hydrogenations, oxidations, for instance ozonolysis, halogenation with gaseous chlorine or fluorine, alkoxylations with gaseous epoxides, addition of hydrogen halides onto double bonds, phosgenations, acidic esterifications, for example with isobutene; or reactions with ammonia.
Microreactors for gas-liquid reactors are, for example, those with continuous phase flow, for instance a falling film microabsorber, and are supplied by various manufacturers on the laboratory scale.
Falling film microabsorbers are based on the principle of the wetting of surfaces or of flat microstructured plates by a liquid film under the influence of gravity. The gas can be conducted over the falling liquid film either in cocurrent or in countercurrent. The falling film plates are cooled from the reverse side, which enables exact temperature control and removal of heat or cold.
A falling film microabsorber as used to date according to the prior art is described, for example, in Ind. Eng. Chem. Res., Vol. 44, No. 25, 2005, page 9751.
This reactor design is enlarged to the pilot scale by arranging many flat plates to form a stack with a common distributor and collector system.
However, the principle of the plate stack brings numerous disadvantages. For example, the manufacture of the plate stack by the required bonding, for example by soldering, welding, adhesive bonding, etc., of the individual plates is complicated and costly. Moreover, this design does not enable effective pressure release.
However, the principle of the plate stack brings numerous disadvantages. For example, the manufacture of the plate stack by the required bonding, for example by soldering, welding, adhesive bonding, etc., of the individual plates is complicated and costly. Moreover, this design does not enable effective pressure release. The apparatus is additionally not dismantleable, for example for cleaning, inspection or for refitting, and the enlargeability to the production scale is limited.
A further variant of a falling film microreactor is the cylindrical falling film microreactor, in which the falling film is generated on the outside of an individual tube.
A disadvantage in this system is the large common gas space around the tubes, which constitutes a safety problem. The arrangement as a falling film tube wetted on the outside causes, moreover, a high level of construction complexity, both for the individual tube and for the arrangement of a plurality of tubes, which limits the enlargeability to the production scale.
It was therefore an object of the present invention to find an improved means of performing gas-liquid reactions in a microreactor, which avoids the disadvantages of falling film microreactors according to the prior art used to date.
Unexpectedly, this object is achieved by the utilization of the principles of microstructured gas-liquid falling film reactors in combination with designs of tube bundle heat exchangers using tubes wetted on the inside instead of flat plates or tubes wetted on the outside.
The present invention therefore provides a tube bundle falling film microreactor for performing gas-liquid reactions, which has    a) at least one vertical falling film tube with    b) a device for distributing the liquid on the inside of the tube and    c) a liquid collecting system, and    d) a device for gas supply and removal.